The goal of these studies is to investigate the motile properties of alveolar macrophages and how the motile behavior of these cells is related to the clearing of bacteria from the lungs. The studies are divided into two parts. First, using the linear under-agarose migration assay, we will measure chemokinesis and chemotaxis in terms of parameters that characterize intrinsic cell properties, and test how well these motile properties of lung macrophages conform to a theoretical model of cell migration (derived from Fick's law). Two experimental approaches will be used. First, using populations of cells, we will measure the random motility coefficient and the chemotaxis coefficient. Second, the motility of individual cells will be recorded with time-lapse video microscopy to determine variables such as cell speed, persistence time and orientation bias. Both approaches will be used to determine how well they agree with each other and with the predictions of the theoretical model. In addition, these intrinsic motile parameters will also be related to certain structures involved in the cell's locomotor apparatus - the cytoskeletal system. The second part of these studies will test the hypothesis that chemotaxis is important in the clearance of bacteria from the lung. Using a mathematical model of lung clearance, we have examined previously published data and shown that a significant degree of alveolar macrophage chemotactic ability is required to account for the observed clearance rate. We will now test this hypothesis experimentally in the rat. With the use of measured motile variables derived in the previous section, we will determine how well the theoretical model of lung bacterial clearance agrees with the experimentally observed values of lung clearance. To further test this model, we will measure the motile parameters of lung macrophages after exposure (in vivo and in vitro) to hyperoxia. The changes in bacterial clearance that are predicted from the measured parameters of exposed cells and the theoretical model will then be compared to the experimentally observed alterations in bacterial clearance after hyperoxia.